A novel approach to the study of hypoxia-ischemia-induced clinical and subclinical seizures in the neonatal rat.

Perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of acute mortality and chronic neurologic morbidity in infants and children. HIE is the most common cause of neonatal seizures, and seizure activity in neonates can be clinical, with both EEG and behavioral symptoms, subclinical with only EEG activity, or just behavioral. The accurate detection of these different seizure manifestations and the extent to which they differ in their effects on the neonatal brain continues to be a concern in neonatal medicine. Most experimental studies of the interaction between hypoxia-ischemia (HI) and seizures have utilized a chemical induction of seizures, which may be less clinically relevant. Here, we expanded our model of unilateral cerebral HI in the immature rat to include video EEG and electromyographic recording before, during and after HI in term-equivalent postnatal-day-12 rats. We observed that immature rats display both clinical and subclinical seizures during the period of HI, and that the total number of seizures and time to first seizure correlate with the extent of tissue damage. We also tested the feasibility of developing an automated seizure detection algorithm for the unbiased detection and characterization of the different types of seizure activity observed in this model.

Long-range nucleosome ordering is associated with gene silencing in Drosophila melanogaster pericentric heterochromatin.

We have used line HS-2 of Drosophila melanogaster, carrying a silenced transgene in the pericentric heterochromatin, to investigate in detail the chromatin structure imposed by this environment. Digestion of the chromatin with micrococcal nuclease (MNase) shows a nucleosome array with extensive long-range order, indicating regular spacing, and with well-defined MNase cleavage fragments, indicating a smaller MNase target in the linker region. The repeating unit is ca. 10 bp larger than that observed for bulk Drosophila chromatin. The silenced transgene shows both a loss of DNase I-hypersensitive sites and decreased sensitivity to DNase I digestion within an array of nucleosomes lacking such sites; within such an array, sensitivity to digestion by MNase is unchanged. The ordered nucleosome array extends across the regulatory region of the transgene, a shift that could explain the loss of transgene expression in heterochromatin. Highly regular nucleosome arrays are observed over several endogenous heterochromatic sequences, indicating that this is a general feature of heterochromatin. However, genes normally active within heterochromatin (rolled and light) do not show this pattern, suggesting that the altered chromatin structure observed is associated with regions that are silent, rather than being a property of the domain as a whole. The results indicate that long-range nucleosomal ordering is linked with the heterochromatic packaging that imposes gene silencing.

The fourth chromosome of Drosophila melanogaster: interspersed euchromatic and heterochromatic domains.

The small fourth chromosome of Drosophila melanogaster (3.5% of the genome) presents a puzzle. Cytological analysis suggests that the bulk of the fourth, including the portion that appears banded in the polytene chromosomes, is heterochromatic; the banded region includes blocks of middle repetitious DNA associated with heterochromatin protein 1 (HP1). However, genetic screens indicate 50-75 genes in this region, a density similar to that in other euchromatic portions of the genome. Using a P element containing an hsp70-white gene and a copy of hsp26 (marked with a fragment of plant DNA designated pt), we have identified domains that allow for full expression of the white marker (R domains), and others that induce a variegating phenotype (V domains). In the former case, the hsp26-pt gene shows an accessibility and heat-shock-inducible activity similar to that seen in euchromatin, whereas in the latter case, accessibility and inducible expression are reduced to levels typical of heterochromatin. Mapping by in situ hybridization and by hybridization of flanking DNA sequences to a collection of cosmid and bacterial artificial chromosome clones shows that the R domains (euchromatin-like) and V domains (heterochromatin-like) are interspersed. Examination of the effect of genetic modifiers on the variegating transgenes shows some differences among these domains. The results suggest that heterochromatic and euchromatic domains are interspersed and closely associated within this 1.2-megabase region of the genome.

Characterization of sequences associated with position-effect variegation at pericentric sites in Drosophila heterochromatin.

In a variety of organisms, euchromatic genes brought into juxtaposition with pericentric heterochromatin show position-effect variegation (PEV), a silencing of gene expression in a subset of the cells in which the gene is normally expressed. Previously, a P-element mobilization screen identified transgenic Drosophila stocks showing PEV of an hsp70-white+ reporter gene; transgenes in many of these stocks map to the chromocenter of polytene chromosome. A screen at an elevated temperature identified two stocks that under standard culture temperatures show complete repression of the hsp70-white+ transgene. The transgenes in both cases map to the chromocenter of polytene chromosomes. Different types of middle repetitive elements are adjacent to seven pericentric transgenes; unique sequences are adjacent to two of the perimetric transgenes. All of the transgenes show suppression of PEV in response to a mutation in the gene encoding heterochromatin protein 1 (HP1). This suppression correlates with a more accessible chromatin structure. The results indicate that a pericentric transgene showing PEV can be associated with different types of DNA sequences, while maintaining a common association with the chromosomal protein HP1.

The silent sinus syndrome. A cause of spontaneous enophthalmos.

PURPOSE: Spontaneous enophthalmos and hypoglobus, in the absence of other symptoms and unrelated to trauma or surgery, may be alarming to both physician and patient. The authors describe the clinicopathologic features of a benign syndrome ("silent sinus syndrome") with this constellation of features and discuss the possible pathophysiology. METHODS: A multicenter retrospective search for similar clinical cases was performed. All clinical records, computed tomographs, and pathology reports for each case were reviewed at one center. A literature search for similar cases also was conducted. RESULTS: Nineteen cases of a new syndrome are presented. This syndrome affects individuals at approximately the fourth decade of life (average age, 36 years; range, 29-46 years); is characterized by bone resorption and remodeling of the orbital floor due to otherwise asymptomatic maxillary sinus disease; is associated with ipsilateral maxillary sinus hypoplasia; and is not fully explained by any previously described, classic cystic lesion of the maxillary antrum. CONCLUSION: Enophthalmos and hypoglobus unassociated with prior trauma, surgery, or other symptoms may represent "silent sinus syndrome," which is ipsilateral maxillary sinus hypoplasia and orbital floor resorption.

Comparison of the accuracy of computerized videokeratography and keratometry for use in intraocular lens calculations.

We compared the accuracy of keratometry and computerized videokeratography (CVK) for use in intraocular lens calculations. We studied 48 eyes of 45 patients having phacoemulsification and posterior chamber lens implantation. Computerized videokeratography was performed with the EyeSys Corneal Analysis System (ECAS). Using the SRK II, SRK/T, and Holladay formulas, we evaluated predictive accuracy calculated with keratometric values and four values derived from ECAS measurements. For each formula, the use of one of the CVK parameters resulted in lower mean absolute errors between actual and predicted postoperative refractive errors and higher percentages of cases with power prediction errors < 0.5 and < 1.0 diopters. Computerized videokeratography may provide a more accurate corneal curvature value than keratometry for use in intraocular lens calculations.